1. Field of the Invention
The present invention relates to a pulsatile pump useable in cardiosurgery for extracorporeal circulation.
2. Discussion of the Background
More particularly, the object of the present invention is to provide a pulsatile pump essentially constituted by a housing chamber, inside which is inserted a length of an elastic hose, which chamber is fitted with two squeeze valves, i.e., a suction valve and a delivery valve, and with an electropneumatically-driven pusher body.
During the past ten years, the importance of inducing extracorporeal circulation which is as "physiologic" as possible was stressed by many studies. In particular, the choice of a pulsatile perfusion instead of a traditional, non-pulsatile perfusion, was regarded as superior as regards the reduction of the peripheral resistances (K. M. Taylor, J. Thorac. Cardiovas. Surg., 75, 569-83 (1978); J. Dunn, J. Thorac. Cardiovas. Surg., 68, 138-47 (1974); and H. Soroff, Arch. Surg., 98, 321-25 (1969)), the rapidity and uniformity of patient cooling and heating (G. D. Williams, J. Thorac. Cardiovas. Surg., 78, 667-77 (1979)), the reduction of the hormonal and methabolic disfunctions (W. F. Bremmer, J. Thorac. Cardiovas. Surg., 75, 392-99 (1978)), and the decrease of cerebral damage (K.M. Taylor, "Effects of pulsatile flow and arterial line filtration on cerebral cellular damage during open heart surgery", Open Heart Surgery, Springer Verlag, Berlino, 1982; and T. Matsumoto, Am. Surg., 1971, 61-64).
The need for realizing a pulsatile perfusion in order to obtain better operative and post-operative patient conditions, is particularly felt in infantile and pediatric cardio-surgery, owing to the greater criticity of the patient.
The use is known of pulsatile-flow pumps, which are obtained by means of suitable modifications supplied to the traditional peristaltic roller-pumps, or by coupling these latter in series to oscillating-flow pumps; such devices produce a so-to-speak "pulsed" flow, but are not in anyway capaole of realizing a truly pulsatile flow, i.e., such a flow as to ideally overlap to the physiologic flow, inasmuch as they do not realize a sufficiently short time rise time of the aortal pressure curve, and in the flow rate curve they show the typical ripples due to the separation of the rollers from the relevant seat. Furthermore, with such devices, the diastolic stroke of the pump necessarily coincides with the systolic stroke thereof, an adjustment of the flow curve during the suction stroke being hence impossible.
Furthermore, from U.S. Pat. No. 4,239,464 a pump is known, which is substantially different from the above discussed pumps, and realizes a truly pulsatile flow, by shifting the fluid column contained inside a length of flexible hose, by squeezing the latter by means of a plate. In order to prevent the reverse flow, at both hose ends two valves are provided, which consist of two plates which do rot squeeze the hose to a complete extent, but cause such a large pressure drop that the possibility of flowing back can be regarded as negligible. The movement of the squeezing plate, as well as the movement of the plates of the valves consists of a pure translation. Furthermore, as disclosed in said patent, it is driven by means of a cam system. By this type of pumps, the impulse frequence and the systolic discharge can be adjusted, and the synchronization with the patient's ECG can be established, whilst the ratio between the systole duration to the duration of the whole cycle, and the positioning of the systole inside said cycle cannot be changed, precisely owing to the system, by means of which the squeezing is accomplished (a system of volumetric type, with the movement drive being controlled by a cam outline).